Enabling extrusion sharpens selected object
The video shows the typical (and not incorrect) bulging that happens when you have a closed tubular object with subdivision surface enabled. To avoid that, delete the face at the end so that the mesh is open on the side where you extrude it. If you want to leave it closed, add a loopcut to sharpen / flatten the bulge. It also helps with the fixed direction so you don't have to hit Z to unlock it. The face normal indicates the direction of the extrude, without it it is not locked at the beginning of the extrusion.